Nanoparticles play several roles in biomedical technology, including as imaging contrast agents, heat sources for photothermal therapy, and as drug delivery vehicles. In many of these applications, nanoparticles are functionalized with specific antibodies for targeting purposes. Ideally, antibodies would be distributed equally among the nanoparticles in a preparation and evenly distributed on each nanoparticle?s surface; however, this is an overly simplistic picture. In reality, there are likely to be variations in the number of antibodies per nanoparticle, their spatial distribution on the surface, and the degree to which their function is preserved. In order to characterize nanoparticle bioconjugates, and to design improved ones, the details of the surface functionalization must be better understood. The following two aims will pave the way towards this goal. (1) The distributions of the number of antibodies per nanoparticle within a nanoparticle preparation will be measured at the single-particle level using microwell array analysis, for both gold and polystyrene nanoparticles. (2) The spatial arrangement of antibodies on the surfaces of individual nanoparticles will be imaged using sub-diffraction-limited fluorescence microscopy. The preparation methods will be optimized to produce nanoparticles with uniform functionalization in terms of the number and spatial distribution of molecules on the surface. Characterizing and optimizing the surface functionalization is important for the development of nanoparticle-based therapies. Improving the uniformity and quality of antibody functionalization will lead to improved targeting. The project will be carried out in the Department of Physics and Astronomy at the University of Texas at San Antonio, which is one of the country?s largest designated Hispanic Serving Institutions. An important part of this SCORE project will be the training of Ph.D. students from groups historically underrepresented in the physical and health sciences, and the elevation of research at this growing institution.